I had my sprinkler system blowing out last fall then this spring when I turned on the water at the manifold the sprinklers came on and now I can't shut them off. What do I do?
This seems to be a common phenomenon. I live in So. Cal. so I don't know much about freezing temperatures and it's effect on valves. My guess would be the diaphragm. Hopefully someone who sees this every spring will chime in.
If your backflow was recently repaired they may have got some debris in the mainline and cloggged a valve. Maybe you can locate the problem valve and take apart and clean debris or replace the guts if you need to.
Try using the flow controller on the valve to reduce the flow and see if that works. Also could be the plunger in the solenoid sticking. You can unscrew the solenoid but be careful that the plunger doesn't pop out as they are spring loaded. Make sure it move freely. If it doesn't get a new solenoid.